A gasoline or diesel engine may include an exhaust gas recirculation (EGR) system to reduce engine NOx emissions and improve vehicle fuel economy. The EGR system may recirculate exhaust gas from an exhaust manifold to an engine intake manifold to dilute charge entering the engine with inert gas. The recirculated exhaust gas may reduce temperatures within engine cylinders to reduce NOx formation. Further, since at least a portion of the recirculated exhaust gas does not participate in combustion within the engine cylinders, the engine may be operated at higher intake manifold pressures, thereby reducing engine pumping losses. However, if the amount of EGR entering engine cylinders is too great, cylinders of the engine may misfire, thereby increasing engine emissions and reducing engine torque output. Therefore, it may be desirable to receive feedback from a sensor that indicates the amount of EGR entering the engine.
One way to determine EGR flow to the engine is to measure a pressure drop across a sharp edge orifice in path between an engine exhaust manifold and an engine intake manifold. The pressure drop may be converted into an EGR flow rate that may be used via a controller to adjust a position of an EGR valve to provide a desired EGR flow rate to the engine. Yet, because exhaust gas may contain soot and other compounds that may accumulate in the exhaust system, it may be possible for the EGR flow sensor to become clogged with matter or for the EGR orifice to become clogged with matter such that the output of the EGR sensor is degraded with respect to reflecting an actual EGR flow rate through the EGR system. Further, if the EGR valve is opened and closed to ascertain EGR system functionality, vehicle occupants may notice a rough running engine. Further still, pressure changes in the exhaust system due to combustion in the engine may influence EGR flow measurements. Therefore, it may be desirable to have a way of diagnosing an EGR system that may determine the presence or absence of EGR system degradation without disturbing vehicle occupants and combustion within the engine.
The inventor herein has recognized the above-mentioned disadvantages and has developed an engine operating method, comprising: increasing air flow through an engine that is not rotating via a controller in response to a request to diagnose operation of an exhaust gas recirculation (EGR) system.
By increasing air flow through an engine that is not rotating, it may be possible to provide the technical result of ascertaining the presence or absence of EGR system degradation without disturbing vehicle occupants or engine emissions. In one example, an electrically driven compressor may be activated to increase air flow through an engine that is not rotating. If air flow through the engine as observed by a particulate filter differential pressure sensor and flow through the engine as observed by an EGR system differential pressure sensor are in agreement, it may be judged that the EGR system is operating in a desired way. However, if air flow through the engine as observed by the particulate filter differential pressure sensor is not in agreement with air flow through the engine as observed by the EGR system differential pressure sensor, then it may be judged that the EGR system is degraded.
The present description may provide several advantages. In particular, the approach may be used to diagnose EGR system operation without disturbing vehicle occupants or degrading vehicle emissions. In addition, the approach may be implemented without increasing system cost. Further, the approach may distinguish between EGR sensor degradation and EGR valve degradation so as to improve diagnostics and reduce rework costs.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.